Method and device for determining the spacing between a first and a second signal sequence

ABSTRACT

The invention relates to a method and a device for determining the spacing between a first sequence of signal values and a second sequence of signal values, wherein a third signal value of the second sequence lying temporally or spatially between the first and second signal values is assigned to one first signal value and second signal value each of the first sequence, which values follow each other in succession, wherein the method comprises the determination of at least one first spacing value based on the following method steps: a) determining a mixing value from the first and second signal values by weighting these signal values; b) determining a mathematical spacing between the mixing value and the third signal value in order to provide a second spacing value; c) determining an interval width value which is dependent on the interval width of an interval defined by the first and second signal values; d) mapping the first spacing value onto the second spacing value using the interval width value as the mapping parameter.

The invention relates to a method and a device for determining the spacing between a first sequence of signal values and a second sequence of signal values, wherein a third signal value of the second sequence lying temporally or spatially between the first and second signal values is assigned to one first signal value and second signal value each of the first sequence, which values follow each other in succession.

First and second signal sequences of this type are obtained, for example, in image processing, when the image information of two temporally sequential fields with offset raster positions built up line by line are read column-by-column. Fields of this type include, for example, interlaced television pictures at a frequency of 50 Hz/60 Hz. The determination of spacing between two signals generated in this manner is necessary, for example, to obtain a gauge as to whether, or possibly by what degree, two successive images or image segments of an image sequence differ. This information is required, for example, to be able to determine whether the image sequence is displaying a so-called still image or sequences of motions. Depending on the result, it is then possible, for example, to select the appropriate algorithms to generate intermediate images.

Due to the difference in raster positions, the two fields cannot be compared pixel for pixel, nor can the signal sequences obtained from column-by-column scanning of the fields be compared signal value by signal value. The problem with interlaced fields is that for the pixel positions to which an image information value is assigned in the first field, there does not happen to be any image information value present in the second field. To each two successive signal values of a first signal sequence obtained through column-by-column reading of a first field, a signal value is assigned from a second signal sequence obtained through column-by-column reading of a second field. The signal value of the second sequence is spatially assigned to the signal values of the first signal sequence by the fact that this value belongs to one pixel position which is located between the pixel positions of the signal values of the first sequence.

A known approach to comparing images image/image segments of this type with different raster positions is to first perform a pixel interpolation procedure so as to be able to assign to each pixel of the field with the first raster position a corresponding pixel in the field with the second raster position, after which a comparison procedure can be implemented once each pixel of a first image has been assigned a pixel at the corresponding position in the second image, in which comparison procedure the two images are compared pixel by pixel, and the quantities of the differences for the image information values assigned to the individual pixels are added up.

The quality of the spacing determination here depends to a significant degree on the quality of the interpolation procedure, and interpolation procedures which perform a reliable pixel interpolation are complex in their implementation.

Other signal sequences in which one signal value of a second signal sequence is assigned to two signal values each of a first signal sequence include, for example, measurement series which are generated by regular measurement of a physical parameter in which the measurement times of the two series are temporally offset—with the result that a measured value of the first series is always recorded temporally between two measured values of the second series, and vice versa. For these signal sequences as well, it is desirable to be able to determine their spacing without the necessity of previously generating interpolated intermediate values for the two series using a complex interpolation procedure.

The goal of the present invention is to provide an effective method for determining the spacing between two signals, specifically for determining the spacing between two signals that define images having different raster positions, which method does not require a complex interpolation procedure. An additional goal of the invention is to provide a device for implementing this method.

This goal is achieved by a method having the features of claim 1, and by a device having the features of claim 11. Advantageous embodiments of the invention are presented in the subclaims.

The method according to the invention for determining a spacing between a first sequence of signal values and a second sequence of signal values, wherein a third signal value of the second sequence located temporally or spatially between the first and second signal values is assigned to one first signal value and second signal value each of the first sequence, which values follow each other in succession, comprises the determination of at least one first spacing value based on the following method steps:

-   -   a) determining a mixing value from the first and second signal         values by weighting these signal values;     -   b) determining a mathematical spacing between the mixing value         and the third signal value to provide a second spacing value;     -   c) determining an interval width value that is dependent on the         interval width of an interval defined by the first and second         signal values;     -   d) mapping the second spacing value onto the first spacing value         using the interval width value as the mapping parameter such         that a mapping curve by which the second spacing value is mapped         onto the first spacing value has at least two segments with         different slopes, whereby the slope of the curve, at least in         segments, is shallower for second spacing values that are         smaller than the interval width value than for the second         spacing values that are larger than the interval value width;         and such that for at least one second spacing value that is         smaller than the interval width value, the assigned first         spacing value is smaller than this second value.

The device according to the invention for determining a spacing between a first sequence of signal values and a second sequence of signal values comprises the following features:

-   -   a mixing unit to generate a mixing value from a first signal         value and second signal value, which follow in succession in the         first signal sequence, by weighting these signal values;     -   a spacing determination unit to which are supplied the mixing         value and a third signal value of the second sequence, which         third value is temporally or spatially assigned to the first and         second signal values, and which unit provides a mathematical         spacing between the mixing value and the third signal value, and         provides a second spacing value therefrom;     -   an interval determination unit to which the first and second         signal values are supplied, and which determines an interval         width of an interval defined by the first and second signal         values, and provides an interval width value therefrom;     -   a mapping unit to which the second spacing value and the [¹]         spacing value are supplied, and which provides the first         interval width value, wherein the mapping unit maps the second         spacing value onto the first spacing value using the interval         width value as the mapping parameter such that a mapping curve         by which the second spacing value is mapped onto the first         spacing value has at least two segments with different slopes,         whereby the slope of the curve, at least in segments, is         shallower for second spacing values that are smaller than the         interval width value than for second spacing values that are         larger than the interval value width; and such that for at least         one second spacing value that is smaller than the interval width         value, the assigned first spacing value is smaller than this         second value.         ¹Translator's note one would expect the word “first” here; OR         this phrase should be adjusted to match claim 1, d) and the         abstract.

The weighting of the first and second signal values during the generation of the mixing value is preferably dependent on the temporal or spatial position of the third signal value relative to the first and second signal values. When the third signal value is located temporally or spatially at the center between the first and second signal values, the mixing value is generated as the mean value of the first and second signal values, although for the sake of simplicity it is also possible to generate the mean value as the mixing value for other temporal or spatial positions of the third signal value. Preferably, the mixing ratio is determined as a function of the temporal or spatial position of the third signal value relative to the position of the first and second signal values. For example, the first signal value is weighted more strongly as compared with the second signal value when the first signal value is located temporally or spatially closer to the third signal value than is the second signal value. Corresponding mixing ratios apply for other positions of these three signal values relative to each other.

The interval width value is preferably chosen so that it corresponds to half the interval width of the interval defined by the first and second signal values.

The present invention will now be described in greater detail based on the figures.

FIG. 1 is a schematic view showing image segments of two successive fields illustrating the generation of first and second signal sequences with signal values that are spatially offset relative to each other;

FIG. 2 is a detailed section from the field sequences of FIG. 1 illustrating the positions of the pixels from the first and second fields relative to each other;

FIG. 3 is a diagram illustrating individual signal values from the first and second signal sequences;

FIG. 4 shows the signal characteristics of different functions for mapping the second spacing value onto the first spacing value;

FIG. 5 shows a first embodiment of a device for determining the spacing between a first signal sequence and a second signal sequence;

FIG. 6 shows a second embodiment of a device for determining a spacing between a first signal sequence and a second signal sequence.

Unless otherwise indicated, the same reference notations in the figures identify components with the same meaning.

The method according to the invention for determining the spacing between two signal sequences is explained below based on a first signal sequence and a second signal sequence that are generated by column-by-column detection of the image information values of an interlaced first and second field. However, the invention is of course not restricted to the determination of the spacing between two such signal sequence for images but may also be applied to any signals for which the signal values are temporally or spatially offset relative to each other.

FIG. 1 is a schematic view of image segments from two successive interlaced fields A, B, in which image information values are assigned only to the pixels from every second line, where these lines with image information values in the two fields are offset relative to each other, as illustrated in FIG. 1 by the fact that in those lines to whose pixels image information values have been assigned the pixels are shown schematically by boxes, while those lines containing no image information are shown as empty lines.

In the case of television transmission, for example, interlaced fields of this type are transmitted at a frequency of 50 Hz/60 Hz. In order to select appropriate interpolation algorithms, for example, in intermediate image interpolation in which intermediate images are generated with respect to existing images, information is required as to whether the existing fields A, B represent moving images or still images. There is no possibility of directly comparing the image information values assigned to the pixels of field A with the image information values assigned to the pixels of field B since the interlaced fields are complementary, and there is in fact no image information assigned to the second field for those pixels to which image information is assigned in the first field.

When the displayed fields A, B, are each read line-by-line, a signal sequence is obtained for each column, whereby one signal value of the second signal sequence is spatially assigned to two signal sequences each of the signal sequences obtained from one of the fields based on the fact that the pixel belonging to the signal value of the second signal sequence lies between the pixels of the two signal values of the first signal sequence—as is illustrated in FIG. 2.

FIG. 2 illustrates individual pixels of fields A and B in a randomly selected column k and in lines i−1, i i+1, i+2. Image information values a(i−1) and a(i+1) are assigned to pixels P(k, i−1) and P(k, i+1) of first field A that lie one below the other in column k. No image information value is assigned to a pixel P(k, i) lying between these pixels P(k, i−1) P(k, i+1) in field A—however, in field B an image information value b(i) is assigned to it. If one considers a signal sequence a(k) generated by reading a column of field A and a signal sequence b(k) generated by reading a corresponding column of field B, then one signal value of signal sequence b(k) is spatially assigned to two signal values each of signal sequence a(k) such that the pixel belonging to the signal value of signal sequence b(k) lies between the pixels of two adjacent signal values of signal sequence a(k). Conversely, one signal value of signal sequence a(k) is accordingly assigned to two signal values of signal sequence b(k). With reference to FIG. 2, the image information value b(i) of signal sequence b(k) is assigned to signal values a(i−1) and a(i+1) which are adjacent in signal sequence a(k), while signal value a(i+1) of signal sequence a(k) is assigned to signal values b(i) and b(i+2) of signal sequence b(k). In video signals, for example, the signal values are luminance values or chrominance values.

In the method according to the invention, first spacing values are determined based on two adjacent first and second signal values of the first signal sequence, and on the temporally or spatially assigned third signal value of the second signal sequence, and these obtained first spacing values are linked, specifically, added in order to obtain a gauge for the spacing between the two signal sequences.

The procedure for determining such a first spacing value is explained below based on FIG. 3, where for the following explanation the signal value a(i−1) is assumed as the first signal value and the signal value a(i+1) is assumed as the second signal value, and where the signal value b(i), of the second signal sequence b(k), assigned to these signal values a(i−1), a(i+1) is assumed as the third signal value.

In FIGS. 3A and 3B, these signal values are plotted upward on a scale for two different scenarios, where in the first case the third signal value b(i) lies inside (FIG. 3A) and in the second case lies outside (FIG. 3B) an interval spanned by the first and second signal values a(i−1), a(i+1).

In order to determine the first spacing value, a mixing value a(i) is first generated from the first and second signal values a(i−1) and a(i+1), which mixing value preferably corresponds to the mean value of these two signal values a(i−1), a(i+1), in other words is expressed by: a(i)=0.5·[a(i−1)+a(i+1)]

The first and second signal values a(i−1), a(i+1) span an interval for which an interval width value m(i) is determined that preferably corresponds to half the interval width, in other words, is expressed by: m(i)=0.5·|a(i−1)−a(i+1)|

In addition, a second spacing value d(i) is generated by determining the spacing between mixing value a(i) and the signal value b(i) of the second signal sequence b(k) assigned to the first and second signal values a(i−1), a(i+1). This second spacing value d(i) is expressed by: d(i)=|b(i)−a(i)|

According to the invention, this second spacing value d(i) is mapped onto the first spacing value using the interval width value m(i) as the parameter such that a mapping curve, by which the second spacing value is mapped onto the first spacing value, has at least two segments with different slopes, whereby the slope of the curve, at least in segments, is shallower for second spacing values that are smaller than the interval width value than for the second spacing values that are larger than the interval value width; and such that for at least one second spacing value that is smaller than the interval width value, the assigned first spacing value is smaller than this second spacing value.

FIG. 4 shows examples of curves f2, f3, f4 of three such mappings which meet these requirements, wherein for the sake of comparison the broken curve f1 illustrates a linear mapping by which the second spacing value d(i) is linearly mapped onto the first spacing value dbd(i).

The mapping illustrated by curve f2 satisfies the relationship: dbd(i)=0 for d(i)<c1·m(i), dbd(i)=g1·(d(i)−c1·m(i)) for d(i)≧c1·m(i), where dbd(i) is the first spacing value, d(i) is the second spacing value, c(i) is a constant greater than zero, and g1 is a constant greater than zero which determines the slope of the curve.

This curve f2 represents a so-called coring characteristic by which the second spacing values d(i) that are smaller than the weighted interval width value d(i) are set to zero, while for the second spacing values that are greater than this weighted interval width value c1·m(i) the first spacing value dbd(i) is determined by multiplying the spacing between second spacing value d(i) and the weighted interval width value c1·m(i) by the factor g1. The weighting factor c1 of interval width value m(i) is preferably less than 1.

If c1 is less than 1 and second spacing value d(i) is less than weighted interval width value c1·m(i), then third signal value b(i) lies safely within the interval spanned by first and second signal values a(i−1), a(i+1). First spacing value dbd(i) is then set to zero since it is assumed that the deviation of third signal value b(i) from the interval center a(i) represented by the mixing value results from the temporal or spatial offset of third signal value b(i) relative to first and second signal values a(i−1) a(i+1).

FIG. 4 shows another mapping curve f3 which fulfills the above requirements, where this mapping satisfies the relationship: dbd(i)=0 for d(i)<c1·m(i), dbd(i)=g1·(d(i)−c1·m(i)) for c1·m(i)≦d(i)≦c2·m(i), dbd(i)=g2·(d(i)−c2·m(i))+g1·m(i)·(c2−c1) for c2·m(i)<d(i), where c2>c1 and g2>g1, and where c1 is preferably less than 1. The term g2 is the slope of this curve f3 in the above segment.

These equations define a mapping curve having three segments with different slopes, wherein second spacing value d(i) is mapped onto a first spacing value dbd(i) from zero as long as second spacing value d(i) is less than the weighted interval width value c1·m(i). For second spacing values c(i) greater than the weighted interval width value c1·m(i), the spacing between second spacing value d(i) and weighted interval width value c1·m(i) is mapped using a weighting factor g1 onto first spacing value dbd(i) so as to generate first spacing value dbd(i). Slope g1 of this segment is shallower than slope g2 of a subsequent segment by which second spacing values d(i) greater than a second interval width value c2·m(i) are mapped onto first spacing value dbd(i).

Curve f4 illustrates another possible mapping curve which satisfies the relationship: dbd(i)=1/m(i)·c3·(d(i))² for m(i)≠0, where c3 is a constant greater than zero which for the graph of FIG. 1 is equal to 1.

When the interval width value is equal to zero, second spacing value d(i), for example, is linearly mapped onto the first spacing value according to the expression dbd(i)=g3·d(i).

A common property of all three curves represented f2, f3, f4 which describe the mapping of second spacing value d(i) onto first spacing value dbd(i) is that they have segments with different slopes, whereby smaller values for second spacing value d(i), specifically, those second spacing values d(i) smaller than interval width value m(i), are weighted more strongly for the generation of first spacing value dbd(i) than are larger second spacing values d(i), specifically, those second spacing values d(i) that are greater than interval width value m(i). Another property applicable to all three represented functions f2, f3, f4 is that for second spacing values d(i) smaller than interval width value m(i) the associated first spacing values dbd(i) are smaller than the second spacing values d(i).

FIG. 5 shows an embodiment of a device for determining a spacing between two signal sequences a(k), b(k) that are generated such that a third signal value of the second sequence lying temporally or spatially between the first and second signal values is assigned to one first and second signal value each of the first sequence.

First and second signal sequences a(k), b(k) are supplied to the device shown in FIG. 5, whereby the device has a sampling device 10 which outputs two successive first and second signal values a(i−1), a(i+1) of signal sequence a(k) at two outputs. Second signal sequence b(k) is supplied to a second sampling device 40 which outputs one signal value each of second signal sequence b(k) at its output, whereby this signal value corresponds to a third signal value that is spatially or temporally assigned to first and second signal values a(i−1), a(i+1) of first signal sequence a(k).

Assuming that first and second signal sequences a(k), b(k) are clocked signals, the signal values of which are synchronized with a first clock signal, first sampling device 10 has appropriate delay elements to provide the signals a(i−1) and a(i+1) isochronally with signal b(i) to second sampling device 40.

In addition, the device has a spacing determination device 20 to which first and second signal values a(i−1), a(i+1) are supplied, and which provides an interval width value m(i) which preferably corresponds to the value of half the interval width of the interval spanned by first and second signal values a(i−1), a(i+1).

In addition, the device has a mixing unit 30 to which first and second signal values a(i−1), a(i+1) are supplied, and which provides a mixing value a(i) which preferably corresponds to the mean value of first and second signal values a(i−1), a(i+1).

In addition, the device has a spacing determination device 50 to which mixing value a(i) and third signal value b(i) are supplied, and which provides a second spacing value d(i) which preferably corresponds to the value of the difference between third signal value b(i) and mixing value a(i).

Interval width value m(i) and second spacing value d(i) are supplied to a mapping unit 60 which maps second spacing value d(i) using interval width value m(i) in the manner explained above onto first spacing value dbd(i). This mapping unit 60 may be implemented, for example, as a lookup table in which, based on the functions explained in FIG. 4, for each second spacing value d(i) an associated first spacing value dbd(i) is stored taking into account parameter value m(i), which first spacing value can be outputted at the output. Mapping unit 60 is followed by a summing unit which adds up multiple first spacing values dbd(i) to output a total spacing value for signals a(k), b(k).

FIG. 6 shows another device for determining a first spacing value, wherein this device 2 has signal-processing branches of analogous construction to the device of FIG. 5, the individual components of which are identified analogously to the circuit components in FIG. 5 with the addition of the letters A or B. The first signal-processing branch, including sampling devices 10A, 40A, interval width determination unit 20A and mixing unit 30A, as well as spacing determination unit 50A, determines one first spacing value dbd1(i) each from the adjacent first and second signal values a(i−1), a(i+1) of first signal sequence a(k), where m1(i) identifies the interval width values associated with first and second signal values a(i−1), a(i+1). The term d1(i) in the above signal-processing branch identifies the difference between mixing value a(i) and third signal value b(i) of signal sequence b(k).

The second processing branch provides a first spacing value dbd(i) from two adjacent first and second signal values b(i), b(i+2) of second signal sequence b(k), and from third signal value a(i+1) of first signal sequence a(k). The term m2(i) at the output of interval determination unit 20B represents the interval width value dependent on first and second signal values b(i), b(i+2). The term b(i+1) at the output of mixing unit 30B represents a mixing value dependent on first and second signal values b(i), b(i+2), while d2(i) at the output of spacing determination unit 50B identifies the value of the spacing between mixing value b(i+1) and third signal value a(i+1).

The sampling units 10A, 40A, 10B, 40B of the two signal-processing branches are matched to each other such that they simultaneously output, synchronized with a clock signal, two successive signal values each of one of the signal sequences and the respectively assigned signal values of the other signal sequences. The first spacing values dbd1(i), dbd2(i) available at the outputs of mapping units 60A, 60B are added to generate a first spacing value dbd1(i) which is dependent on four signal values, specifically, two adjacent signal values of first signal sequence a(k) and two adjacent signal values of second signal sequence b(k), whereby one of the two adjacent signal values of the second signal sequence is temporally or spatially assigned to the two adjacent signal values of the first signal sequence.

List of Reference Notations

-   10 sampling unit -   10A, 10B sampling unit -   20 interval determination unit -   20A, 20B interval determination unit -   30 mixing unit -   30A, 30B mixing unit -   40 sampling unit -   40A, 40B sampling unit -   50 spacing determination unit -   50A, 50B spacing determination unit -   60 mapping unit -   60A, 60B mapping unit -   70 adding unit -   a(k) first signal sequence -   b(k) second signal sequence 

1. Method for determining the spacing between a first sequence of signal values (a(k)) and a second sequence of signal values (b(k)), wherein a third signal value (b(i)) of the second sequence (b(k)) lying temporally or spatially between the first and second signal values (a(i−1), a(i+1)) is assigned to one first signal value and second signal value each (a(i−1), a(i+1)) of the first sequence, which values follow each other in succession, wherein the method comprises the determination of at least one first spacing value (dbd(i)) based on the following method steps: a) determining a mixing value (a(i)) from the first and second signal values (a(i−1), a(i+1)) by weighting these signal values (a(i−1), a(i+1)); b) determining a mathematical spacing between the mixing value (a(i)) and the third signal value (b(i)) in order to provide a second spacing value (d(i)); c) determining an interval width value (m(i)) which is dependent on the interval width of an interval defined by the first and second signal values (a(i−1), a(i+1)); d) mapping the first spacing value (d(i)) onto the second spacing value (dbd(i)) using the interval width value (m(i)) as the mapping parameter such that a mapping curve (f2, f3) by which the second spacing value (d(i)) is mapped onto the first spacing value (dbd(i)) has at least two segments with different slopes, whereby the slope of the curve, at least in segments, is shallower for second spacing values (d(i)) that are smaller than the interval width value (m(i)) than for second spacing values (d(i)) that are larger than the interval value width (m(i)); and such that for at least one second spacing value (d(i)) that is smaller than the interval width value (m(i)), the assigned first spacing value (dbd(i)) is smaller than the second spacing value (d(i)).
 2. Method according to claim 1, wherein the interval width value (m(i)) corresponds to half the interval width of the interval defined by the first and second signal values (a(i−1), a(i+1)).
 3. The method of claim 1, wherein the mixing value (a(i)) is the mean value of the first and second signal values (a(i−1), a(i+1)).
 4. The method of claim 1, wherein the mapping satisfies the following relationship: dbd(i)=0 for d(i)<c1·m(i), dbd(i)=g1·(d(i)−c1·m(i)) for d(i)≧c1·m(i), where dbd(i) is the first spacing value, d(i) is the second spacing value, m(i) is the interval width value, c1 is a constant greater than zero, and g1 is a constant greater than zero.
 5. The method of claim 4, wherein c1<1 or c1>1.
 6. The method of claim 1, wherein the mapping satisfies the following relationship: dbd(i)=0 for d(i)<c1·m(i), dbd(i)=g1·(d(i)−c1·m(i)) for c1·m(i)≦d(i)≦c2·m(i), dbd(i)=g2·(d(i)−c2·m(i))+g1·m(i)·(c2−c1) for c2·m(i)<d(i), where c2>c1 and g2>g1, and dbd(i) is the first spacing value, d(i) is the second spacing value, m(i) is the interval width value, c1 is a constant greater than zero, c2 is a constant greater than zero, g1 is a constant greater than zero, g2 is a constant greater than zero.
 7. The method of claim 1, wherein the mapping satisfies the following relationship: dbd(i)=1/m(i)·c3·(d(i))² for m(i)≠0, where dbd(i) is the first spacing value, d(i) is the second spacing value, m(i) is the interval width value, c3 is a constant greater than zero.
 8. The method of claim, wherein the mapping for m(i)=0 satisfies the following relationship: dbd(i)=g3·d(i) where g3 is a constant.
 9. The method of claim 7, wherein multiple first spacing values (dbd(i); dbd1(i), dbd2(i)) are generated based on signal values of the first and second signal sequences (a(k), b(k)), and these first and second signal values are linked to determine the spacing of the signal sequences.
 10. Method according to claim 9, wherein the multiple first spacing values (dbd(i); dbd1(i); dbd2(i)) are added.
 11. Device for determining a spacing between a first sequence of signal values a(k) and a second sequence of signal values b(k), comprising: a mixing unit to generate a mixing value a(i) from a first signal value and a second signal value a(i−1), a(i+1), which follow in succession in the first signal sequence, by weighting these signal values a(i−1), a(i+1); a spacing determination unit to which are supplied the mixing value a(i) and a third signal value b(i) of the second sequence b(k), which third value lies temporally or spatially between the first and second signal values a(i−1), a(i+1), and which unit provides a mathematical spacing between the mixing value a(i) and the third signal value b(i), and provides a second spacing value d(i) therefrom; an interval determination unit to which the first and second signal values a(i−1), a(i+1) are supplied, and which determines an interval width of an interval defined by the first and second signal values a(i−1), a(i+1), and provides an interval width value m(i) therefrom; a mapping unit to which the second spacing value d(i) and the interval width value m(i) are supplied, and which provides a first spacing value dbd(i) wherein the mapping unit maps the second spacing value d(i) onto the first spacing value dbd(i) using the interval width value (m(i)) as the parameter such that a mapping curve by which the second spacing value d(i) is mapped onto the first spacing value dbd(i) has at least two segments with different slopes, whereby the slope of the curve, at least in segments, is shallower for second spacing values d(i) that are smaller than the interval width value m(i) than for the second spacing values d(i) that are larger than the interval value width m(i); and such that for at least one second spacing value that is smaller than the interval width value m(i), the assigned first spacing value dbd(i) is smaller than the second spacing value d(i).
 12. Device according to claim 11, wherein the interval width value m(i) corresponds to half the interval width of the interval defined by the first and second signal values a(i−1), a(i+1).
 13. Device according to claims 11, wherein the mixing value a(i) is the mean value of the first and second signal values a(i−1), a(i+1).
 14. Device according to one of claims 11, wherein the mapping performed by the mapping unit satisfies the following relationship: dbd(i)=0 for d(i)<c1·m(i), dbd(i)=d1·(d(i)−c1·m(i)) for d(i)≧c1·m(i), where dbd(i) is the first spacing value, d(i) is the second spacing value, m(i) is the interval width value, c1 is a constant greater than zero, and g1 is a constant greater than zero.
 15. Device according to claim 14, wherein c1< or c1>0.
 16. Device according to claims 11, wherein the mapping performed by the mapping unit satisfies the following relationship: dbd(i)=0 for d(i)<c1·m(i), dbd(i)=g1·(d(i)−c1·m(i)) for c1·m(i)≦d(i)≦c2·m(i), dbd(i)=g2·(d(i)−c2·m(i))+g1·m(i)·(c2−c1) for c2·m(i)<d(i), where c2>c1 and g2>g1, and dbd(i) is the first spacing value, d(i) is the second spacing value, m(i) is the interval width value, c1 is a constant greater than zero, c2 is a constant greater than zero, g1 is a constant greater than zero, g2 is a constant greater than zero.
 17. Device according to claim 11, wherein the mapping performed by the mapping unit satisfies the following relationship: dbd(i)=1/m(i)·c3·(d(i))² for m(i) ≠0, where dbd(i) is the first spacing value, d(i) is the second spacing value, m(i) is the interval width value.
 18. Device according to claim 17, wherein the mapping for m(i)=0 satisfies the relationship: dbd(i)=g·d(i) where g is a constant. 